Conventionally, methods of imparting bactericidal effects and antibacterial effects to the laundry during washing have been known. Patent Literatures 1 to 9 describe a method of adding hydrogen peroxide or a compound which generates hydrogen peroxide in water to a liquid laundry detergent composition for clothing, a method of using bleaching activator(s) together with the composition, and a method of adding antibacterially active cationic agent(s) such as quaternary ammonium salts and polyaminopropyl biguanide salts or antibacterially active inorganic agent(s) such as water-soluble silver.
However, in the case of a liquid laundry detergent composition for clothing containing hydrogen peroxide or a compound which generates hydrogen peroxide in water, it has less long-term stability and cannot be expected to exhibit bactericidal effects and antibacterial effects over a long period of time.
In the case of a liquid laundry detergent for clothing containing antibacterially active cationic agent(s) such as quaternary ammonium salts and polyaminopropyl biguanide salts, the active agents are immediately adsorbed into the coexisting laundry during washing and cannot attack the bacteria lurking in the water between the fibers. They cannot sufficiently exhibit bactericidal effects, accordingly. Furthermore, the capacity of washing machines has recently increased, and a lot of laundry is more often packed into a washing machine to wash together. When the laundry packed into the washing machine is washed, antibacterially active cationic agents cannot sufficiently reach the inside of the fibers, and cannot be expected to exhibit bactericidal effects and antibacterial effects at all. Furthermore, some antibacterially active cationic agents may react with chlorine in tap water, which deteriorates the antibacterial activity of the agents or may yellow white cotton fibers. In the case of a liquid laundry detergent composition for clothing containing water-soluble silver, it has a problem of poor stability.
In recent years, considering the influence on the environment, use of the hot water left in the tub after taking a bath to do the laundry has tended to increase, and it has been confirmed that not less than 60% of households use the hot water left in the tub after taking a bath to do the laundry throughout a year. This is because that in addition to the advantage of saving water, washing at a higher temperature improves cleaning efficiency. However, the hot water left in the tub after taking a bath comprises a lot of microorganisms and dirt from human bodies and the environment, and the number of bacteria in the water kept overnight from bathing reaches as many as 106 to 107/ml. Therefore, use of the hot water left in the tub after taking a bath as water to do laundry also causes an increased number of bacteria in the laundry. For this reason there is need for a technology exhibiting a higher bactericidal effect which can reduce the number of bacteria in the reaming hot water and the number of bacteria attached to the laundry in a short period of time to do the laundry with the hot water in the tub after taking a bath.
Further, in the case of room-drying the laundry, which follows washing with the hot water left in the tub after taking a bath, thereby the laundry being kept under a high humidity condition for a long period of time, which is a suitable environment for the growth of residual bacteria, it is a cause of unpleasant damp-dry odor, also called room dry smell. Therefore, in order to suppress the growth of bacteria in the clothing after washing, there is need for a technique of imparting a higher antimicrobial effect than conventional ones.
Patent Literatures 9 and 10 disclose that liquid laundry detergent compositions for clothing containing a quaternary nitrogen-containing polymer prevents a damp-dry odor of the clothing caused by room-drying, and imparts a dirt release effect. However, they do not describe at all that the compositions impart the bactericidal effect during washing.
The term “bactericidal” herein means eliminating, through bactericidal activities, bacteria which have already attached to the laundry and grown prior to washing. The term also means reducing the number of bacteria in the laundry during doing the laundry with the hot water left in the tub after taking a bath. The term “antibacterial” means that the active ingredient which remains on the laundry exhibits the activities to inhibit the proliferation of bacteria.